In typical dry-type electrophotographic processes, latent electrostatic images formed on a photoconductor are developed by means of a triboelectrically charged toner. Specifically, when an image is formed by a photographic copying machine, a surface of a roller composed of a photoconductive and photosensitive material is charged. An electrostatic latent image is formed by exposure to the light reflected from the surface of an original to be copied. The latent image is developed by a toner, with the formed visible image being transferred to a paper or the like. The transferred image is fixed on the paper by compression under heating, and thus a copy print is obtained.
A typical toner includes several components including a toner resin, a colorant and an electrostatic carrier material. The toner resin is of particular importance in that it seines to bind the other two components. Typically, toner resins are formed from various materials, such as bisphenol epoxy resins, silicone-based resins, styrene butadiene resins, and the like.
One of the problems associated with the fixing of toner is the undesirable transfer of toner to the fusing roller during the fixing process. This undesirable transfer is sometimes referred to as “off setting” and involves the transfer of toner from the substrate to the fusing roller. The transfer of toner to the fusing roller contaminates the fusing roller, which results in the unwanted transfer of toner from the fusing roller onto subsequent substrates passing by the fusing roller. This transfer tends to produce ghost images or unwanted toner marks on subsequent substrates.
The use of crosslinked polyester to prevent offset is generally known. A crosslinked polyester is typically obtained by reacting an esterified bisphenol A (Bis A) with dicarboxylic acid to produce a linear polyester, and then reacting the produced linear polyester with trivalent or higher carboxylic acid, such as trimellitic acid anhydride.
However, due to the relatively high cost of Bis A and the environmental and toxicity concerns associated with Bis A, it would be desirable to develop toner resins that do not include Bis A, or include reduced amounts of Bis A. However, currently available Bis A-free toner resins, e.g., those described in U.S. Pat. No. 5,015,724 to Kawabe, may have undesirable properties, such as brittleness and relatively poor heat resistance. Therefore, it would be desirable to develop toner resins that reduce or eliminate the use of Bis A, yet still have desirable toner resin properties.